Swaleage

August 3rd, 2015. Post by Quinta do Vale

It’s been a long time since this blog was last updated. Those keeping up with us on Facebook will have some inkling of what’s been going on at the quinta in the meantime, but I’ve failed dismally at getting to the more detailed documentation of it all. Mostly a case of too busy doing the doing to be reporting the doing …

Following the successful implementation of a swale system on the bottom terrace last year, this last Spring I put in a similar system on the terrace above it. It’s a narrow terrace with very similar problems to the one below it – soil so dry in summer it barely supported a few fruit trees (which consequently dropped most of their fruit before it got anywhere near ripe) amongst grasses and wildflowers which would be dry and dead by July. In summer, the soil turned to dust in your hand and blew away.

Mid fruit terrace

The terrace when we first saw the quinta in November 2008 – a few neglected fruit trees and a lot of encroaching bracken

Mid fruit terrace

The same terrace in May last year – a few more fruit trees, a lot less bracken, but still a largely barren terrace

A simple solution to the terrace’s immediate problems would have been to clear the grasses from around the trunks of the fruit trees, mulch heavily and install drip line irrigation to the trees, but the underlying aim of much of the work here has been to improve the water-holding capacity, life and health of the soil to a point where irrigation becomes only minimally necessary.

Grass-clearing and mulching around the trees had already been done. The next step was to address the soil.

In common with most of the terracing on the quinta, the flatter land that’s been created for growing is still far from being flat. Gradients have been reduced from between 30-45°, but average 18-22° over the terraces themselves. On this terrace, as with the one below it, contour lines run diagonally from the edge of the terrace to the slope or wall behind it. This means the terrace surface slopes in a different direction to the mountain slope it’s created from, which runs perpendicular to the line of the terrace itself.

This is ingenious. It makes for a reasonably gradual slope along the line of the terrace and directly across it (see image below), so rainwater run-off is not lost as rapidly as it would otherwise be. Flowing diagonally, it spreads and spends much longer crossing the surface of the terrace, but still drains effectively without channeling or eroding terrace walls. Surprisingly, the average annual rainfall here – 1040mm – is slightly more than where I used to live in the very wet Scottish Borders, but just about all of it falls in the winter months, so effective drainage is no less critically important as water retention is for the summer months.

Mid fruit terrace

Looking along the terrace. It’s deceptive. The gradient appears quite slight both along and across the terrace. It’s far from that, as can be seen in the following images

The existing fruit tree plantings however had been made following the line of the terrace, so the trick with the swales would be to space them in such a way as to leave no tree without a swale close enough behind it to irrigate it.

Since these swales won’t be fed by ponds like the terrace below, the idea is to fill them by hosepipe every 7-10 days through the summer drought, decreasing the frequency of irrigation as the soil improves year on year. To begin with, plantings will be limited to mulched swale berms so as not to place too much demand on water supplies through the summer, especially as the winter rains failed during the winter of 2014-15.

Mid fruit terrace swale

The first swale. This was dug wide enough to form a pathway a comfortable wheelbarrow’s width

We had worn a well-compacted pathway along the middle of the terrace simply by walking along it frequently, so the first task was to create a new pathway and decompact as much as possible of the old. The narrowest part of the terrace is simply not wide enough to have room for both swale and pathway between the trees, so the logical solution was to make the swale itself into a path. With the contour lines running diagonally, this would result in the path meeting the back slope before it reached half way along the terrace. This turned out to be less of a problem than it first seemed – it was simple enough to end the swale at the back slope, then continue the path along the back of the terrace.

Mid fruit terrace swales

The path along the back of the terrace extending from the first swale. A second narrower swale is filled with water here to check its level. From this angle, the true gradient of the terrace is much more obvious. The original pathway can still be seem along the middle of the terrace

Mid fruit terrace swales

The first two swales dug and the line of the third marked

Mid fruit terrace swale

The first swale is filled with pine bark. It’s absorbent and holds water well at the same time as providing a firm surface to walk or run a wheelbarrow along

Mid fruit terrace swales

Swales 2, 3 and 4. The fruit trees on the swale berms are interplanted with berry bushes, comfrey and self-seeding annuals like Calendula, Lupins and Brassicas. Bush beans and sweet potatoes will follow as the weather warms up

Mid fruit terrace swales

Swales 2, 3 and 4 from the other direction, again showing a better indication of the gradient of the terrace

Mid fruit terrace swales

The end of the first swale (right) and the remaining 4

Mid fruit terrace swales

The top swale pathway at the end of May

Mid fruit terrace swales

By mid July, the benefit of the swales is clear. The grass beyond their reach is dry and brown while the grass downslope of them is still green

A small amount of compost was spread along the swale berms before planting and mulching.

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2 Responses to “Swaleage”

  1. Linda Morrison Says:

    Wow! I just discovered your blog and am so glad to see that someone else is working with swales on steep terraced land. I am in the foothills of the Sierra Nevada mountain range, near Granada, in Spain. I´ve also started experimenting with swales on my terraces and the documentation of your work is very helpful for figuring out how to do this. Thanks a million!!

  2. Corazon Cook Says:

    Thanks for posting. I will use your swale ideas to my steep farm.

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